Some of the many considerations in designing apparatus for vertical slab gel electrophoresis are cooling to maintain uniform and constant temperature, the maintenance of a steady and uniform electric field, minimizing the volumes of buffer solutions needed, and loading samples in a reliable and reproducible manner.
Gel slabs are usually formed by joining two glass plates together with spacers at both vertical edges to establish a gap between them usually measuring 0.25-3 mm in width. The plates are clamped together along the vertical edges and a seal is placed along the open bottom edge. The gap is then filled with gel solution and a well-forming insert, referred to in the industry as a "comb" or a "template," is placed along the open upper edge with teeth extending into the space between the plates. The gel is allowed to set with this insert in place, and the insert is then removed to leave a row of wells along the top edge of the gel. Samples are placed in these wells after the seal along the bottom edge of the gel is removed and the resulting "gel sandwich" is placed in a cell. Then, the upper and lower exposed edges are placed in contact with conductive buffers in which electrodes are also immersed.
Thin gels are desirable for many separations. Unfortunately, thin gels have thin sample wells, which limit the volume of sample which can be loaded, and also make it difficult to place the sample in the well.
Another problem addressed herein is one which arises with all types of electrophoresis-joule heating. As in other electrophoretic systems, slab gel systems are susceptible to this heating effect, particularly when a high-strength electric field is used. As is well known among those skilled in the art, uncontrolled joule heating can cause damage to the samples, and nonuniform temperatures will cause proteins at different locations of the gel to migrate at different speeds.